Crystallization ability of poly(lactic acid) block segments in templating poly(ethylene oxide-b-lactic acid) diblock copolymers affects the resulting structures of mesoporous silicas

Abstract

In this study we employed poly(ethylene oxide-b-lactide) (PEO-b-PLA) diblock copolymers as templates to prepare mesoporous silica materials. Small-angle X-ray scattering, transmission electron microscopy, and N₂ adsorption/desorption isotherms revealed that the mesostructures of these mesoporous silicas were influenced by both the tetraethyl orthosilicate content and the volume fraction of the PLA block segment. These effects led to the formation of a variety of composition-dependent mesoporous structures, including hexagonally packed cylinders, face-centered cubic-packed spheres, and disordered spherical micelle structures. When using poly(ethylene oxide-b-L-lactide) (PEO-PLLA) diblock copolymers as templates, crystallization of the PLLA block segments was preferred over microphase separation of the block copolymer; accordingly, only lamellar mesoporous structures were formed through crystallization of the PLLA block segment. As a result, eliminating the crystallization ability of PLLA block segments through use of amorphous PLA block segments allowed us to obtain a series of long-range-ordered mesoporous silica materials. As a result, the crystallization ability was the key effect for preparation of highly ordered mesoporous silicas having large pores templated by the PLLA block segment.